Physical therapists have long utilized therapeutic ultrasound because of its thermal and mechanical effects on tissue. Ultrasound (sound at a frequency greater than approximately 20 KHz.) can be produced by applying an alternating electrical current, at the desired frequency, to a transducer incorporating a piezoelectric crystal. The current causes the shape of the crystal to oscillate between a resting state and a different state, thereby producing a sonic wave. The sonic wave can be continuous or pulsed, depending on how the transducer is driven.
Typical indications calling for ultrasonic therapy include tendinitis, bursitis, carpal tunnel syndrome, neck pain and lower back pain. Continuous ultrasound is typically used when thermal effects are desired, for example to reduce muscle spasm. On the other hand, pulsed ultrasound is often preferred for treatment where heat exacerbates pain in the patient, or when only non-thermal, mechanical effects of ultrasound, e.g. enhancement of tissue regeneration, are desired.
In transdermal ultrasonic therapy, a coupling gel is used between the transducer and the patient's skin to eliminate any layer of air, and thereby reduce reflections resulting from the difference in the acoustical impedances of air and the transducer. Typical coupling agents are mineral oil, glycerin, propylene glycol, water and water-based gels.
Ultrasonic therapy is widely used, but for effective treatment, it has generally been necessary to apply ultrasonic energy either at a high intensity or for long intervals of time, or both. An important object of this invention is to provide a method for carrying out ultrasonic therapy in which the transmission of ultrasonic energy through the patient's skin is enhanced.